1. Field of the Invention
The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor device in which supply of power supply voltage to a signal processing circuit can be stopped. In this specification and the like, a semiconductor device refers to all types of devices which can function by utilizing semiconductor characteristics; an electro-optical device, a light-emitting display device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
In recent years, a reduction in power consumption of an electronic device in operation has been highly required. In order to reduce power consumption of an electronic device, operation of each logic circuit is controlled in accordance with operation of a signal processing circuit.
In a voltage regulator, which is an example of a signal processing circuit, a three-stage structure operation with a high power supply rejection ratio and favorable transient response characteristics and a two-stage structure operation with low current consumption are automatically switched (see Patent Document 1). The three-stage structure includes a first differential amplifier circuit, a second differential amplifier circuit, and an output transistor, and the second-stage structure includes the second differential amplifier circuit and the output transistor.